This invention relates to a superconducting metal oxide film and a method of preparing same.
REBa.sub.2 Cu.sub.3 O.sub.7 (RE: Y or a rare earth element) metal oxide superconductors are known to have a common crystal structure and are generally termed 123 superconductor materials. Typical example of such a superconductor is YBa.sub.2 Cu.sub.3 O.sub.7. Among various 123 superconductor materials, a bulk of NdBa.sub.2 Cu.sub.3 O.sub.7-d prepared by an OCMG (oxygen controlled melt growth) method is known to exhibit an excellent critical current density (Jc characteristics) in a high magnetic field. A superconducting film of NdBa.sub.2 Cu.sub.3 O.sub.7-d prepared by an MBE (molecular beam epitaxy) method is disclosed in Appl. Phys. Lett. 57 (26), p2850-2852 (1990). A method of producing a c-axis oriented film of NdBa.sub.2 Cu.sub.3 O.sub.7-d by the MBE method utilizing NO.sub.2 as an oxidizing gas is disclosed in Appl. Phys. Lett. 59 (5), p600-602 (1991).
One serious problem of the known NdBa.sub.2 Cu.sub.3 O.sub.7-d superconducting film is that the superconductive critical temperature Tc (resistance: zero) thereof is as low as about 30 K.